Effect of duration of exposure to sewage sludge-treated pastures on liver tissue accumulation of persistent endocrine disrupting compounds (EDCs) in sheep

Liver tissue concentrations of selected polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) were determined in groups of Texel ewes and lambs following exposure to pastures fertilised with either sewage sludge (Treated; T) or inorganic fertiliser (Control; C). Lambs were slaughtered at the age of 6 months, in each of 3 years, while ewes were slaughtered at 5 to 6 years of age having been exposed to the respective pastures for approximately 6, 18 or 30 months, during the same, respective years, immediately before slaughter. Mean liver concentrations of very few of the chemical classes were elevated in either ewe or lamb tissue as a result of exposure of the animals to sewage sludge. Mean concentrations, in lamb liver, of chemicals of each of the classes differed significantly, but inconsistently, between years, reflecting temporal variations in exposure, although the pattern of annual change differed with individual chemical. On the other hand, in ewes, liver concentrations of many chemicals increased, significantly and consistently, with increasing duration of exposure. It was concluded that the increases in tissue concentrations with increased duration of exposure were unlikely to be sufficient to be of concern to consumers and that tissue burdens cannot be linked, easily, with the physiological effects reported previously for animals similarly exposed.